ESTIMATION OF THE ZEOLITE CONTENTS OF TUFFACEOUS SAMPLES FROM THE BIGADIC CLINOPTILOLITE DEPOSIT, WESTERN TURKEY

Variation of the NH4+-exchange and CO2-adsorption capacities with zeol ite content was investigated in detail to assess the potential use of these capacities for the estimation of the zeolite contents of the sam ples taken from the Bigadic clinoptilolite deposit in western Anatolia , as an alternative to the widely used semi-quantitative X-ray diffrac tion (XRD) technique. Samples with known clinoptilolite contents taken from 2 different zones with fine- and coarse-grained tuffs of the Big adic deposit were used for this purpose. Na-enriched forms of the samp les were prepared by repeated ion-exchange with NaCl solutions, and NH 4+-forms by repeated Na exchange followed by NH4+ exchange with NH4Cl solutions, which in turn were calcined to obtain the H-forms. NH4+-exc hange capacities by Kjeldahl analyses of the NH4+-forms and CO2 adsorp tion isotherms in the 0 to 100 kPa range of Na- and H-forms of the sam ples were determined. Dubinin-Astakhov model parameters were calculate d from the isotherm data. A strong relationship exists between the exp erimental CO2-adsorption capacities at 100 kPa of the Na-forms and the zeolite contents of the samples. Although the Dubinin-Astakhov model represented the isotherm data quite well, the relationships between th e amounts of adsorbate at saturation pressure, calculated from the mod el, and the zeolite contents of the samples were weaker. The strength of the relationship between NH4+ exchange capacities and zeolite conte nts was seen to vary with the zone of origin. There is a very strong r elationship between the adsorption and ion-exchange capacities of the samples in their Na-forms taken from the fine-grained zone, indicating that either ion-exchange or adsorption capacity measurements can be u sed to estimate the zeolite contents of the samples taken from this zo ne, whereas, significant diffusion hindrance was observed against ion- exchange of hydrated cations from aqueous solutions for some samples f rom the coarse-grained zone. Inspection of the data pointed to systema tic errors in the zeolite contents determined by a semi-quantitative X RD technique. When both zones are considered together, CO2-adsorption capacities at 100 kPa of the samples in their Na-forms can be used as a reliable measure of the zeolite content, which in turn is an importa nt index to predict the performance of natural samples in various appl ications.